Hypoxia Impairs Neuromuscular Function More Than Heat After Incremental Test to Exhaustion.

Abstract

Heat stress and hypoxia impair athletic performance through inflammation, muscle injury, and neuromuscular dysfunction. This study examined these effects in 15 endurance athletes (13 males and 2 females, VO_2max=59.5±3.9 ml/min/kg) performing incremental load tests to exhaustion under normal (CON), hypoxic (HYP), and high-temperature and humidity (HOT) conditions. Pre- and postexercise assessments, including blood biomarkers, performance, and surface electromyography (sEMG) during the counter-movement jump (CMJ) and isometric mid-thigh pull (IMTP), were conducted under normal conditions. Compared to CON, time to exhaustion was significantly reduced in HYP and HOT (p<0.05). CMJ performance declined under CON and HYP (p<0.05). Force at 200 and 250 ms decreased under both CON and HYP during IMTP (p<0.05). The root mean square (RMS) and the median power frequency (MPF) were decreased under HYP during CMJ and IMTP (p<0.05). In contrast, no significant differences in sEMG and kinetic markers were observed in the HOT (p>0.05). No significant changes in creatine kinase and lactate dehydrogenase levels were observed (p>0.05). Postexercise, tumor necrosis factor-alpha was lower in HYP (p<0.05), while interleukin-6 increased in HOT (p<0.05). Hypoxia impairs neuromuscular function and suppresses inflammation, whereas heat stress induces inflammation without neuromuscular deficits.